Need exception highlighting on failed import/export in Dialog

[kalemas]

By the way the exception happened should be logged instead of handling stack at

animation_cache/animation_cache/cache_manager.py

Line 155 in 0bf80b7

logger.warn('{}: Cache not writen {} due to exception: \n{}'.format(

-                     logger.warn('{}: Cache not writen {} due to exception: \n{}'.format(
-                         self, c, traceback.format_exc()
-                     ))
+                     logger.warning('{}: Cache not writen {} due to exception:'.format(
+                         self, c, 
+                     ), exc_info=True)